I. Field
The subject specification relates generally to wireless communications, and particularly to transmission of uplink control and data code symbols that span a one or more transmission time intervals.
II. Background
Wireless communication has penetrated nearly every aspect of a person's daily routine. To facilitate work/office activities as well as leisure activities, wireless systems are widely deployed to provide various types of communication content such as voice, data, video, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA), and orthogonal frequency division multiple access (OFDMA) systems.
As users demand more of such wireless systems, third generation long term evolution (3G LTE) systems have emerged as a new generation of wireless environments that can offer high-speed data rates, higher capacity, reuse of legacy platforms/systems, and low latency. The latter is among a key element in providing a superior user experience, or quality of service, among market segments with high consumption potential. Specific applications such as multi-player on-line gaming and remote virtual office deployments require low latency communications, and users can gravitate toward service providers that deliver such low-latency services.
To attain low latency, while maintaining low complexity and efficient power use at the user equipment, 3G LTE systems rely on asymmetric communication links: Forward link (or downlink) uses orthogonal frequency division multiple access, where transmission is effected by sending data and control code symbols on a plurality of subcarriers in order to increase data rates and cell capacity; and reverse link (or uplink) employs single-carrier frequency division multiple access, which affords low peak-to-average power ratio and the ensuing efficient use of power resources at the terminal. Thus, any advance on data rate and capacity increase, as well as latency needs to preserve such characteristics of the downlink and uplink. In particular, to lower latency there is a need to transmit DL data/control code symbols with short transmission time intervals (TTIs), while receiving UL control code symbols transmitted in SC-FDMA with sufficiently long TTIs (typically longer that DL data TTI) so as to adequately convey control information, e.g., channel quality indicators, interference levels, terminal capabilities and conditions, . . . . Increased terminal and processing complexity can be acceptable depending on the gains in reducing latency.